The present invention relates generally to an end turn bracing apparatus and, more particularly, to a bracing device which provides a means for correcting misalignment which permits the apparatus to be periodically retightened.
Many dynamoelectric machines utilize a stator coil configuration comprising two coaxial groups of conductors with each stator slot having an inner and an outer coil disposed therein. These two cylindrical associations typically extend axially outward from each end of the dynamoelectric machine and radially outward from its central axis. This formation results in an end turn configuration which comprises two coaxial conical coil associations in which the inner and outer coil groups diverge as they progress axially from the stator structure.
The end turn region of a stator coil is subjected to potentially severe vibrations due to its cantilevered configuration and the rotation of the rotor of the dynamoelectric machine and its resulting rotating magnetic field. Many bracing schemes have been tried in the past. For example, U.S. Pat. No. 3,344,296 issued to Coggeshall et al. on Sept. 26, 1967 uses a tension strap to exert a radially outward force on an inner conical coil configuration in order to provide a bracing system which can withstand the above-mentioned vibrational forces. Similarly, U.S. Pat. No. 2,994,735 issued to Marshall et al. on Aug. 1, 1961 lashes the end turns to hoop-like binding bands with a plurality of ties which prevent movement of the individual end turn conductors.
In U.S. Pat. No. 3,344,297 issued to Bishop et al. on Sept. 26, 1967, a J-shapped bar is shown being disposed around the radially inward surface of a ring and passing radially outward between an end turn configuration to be connected to an axial support member by means of a bolted connection. In a somewhat similar disposition, a band is utilized to provide a radially outward force on conical end turns in U.S. Pat. No. 3,949,257 issued to Cooper et al. on Apr. 6, 1976.
Many techniques are available to restrain the movement of the end turn region of stator coils which include providing either a radially outward force on the end turns or a compressing force which pulls the inner and outer conical end turn arrays together. Other examples of these methods are disclosed and described in U.S. Pat. No. 1,238,280 issued to Field on Aug. 28, 1917; U.S. Pat. No. 3,348,085 issued to Coggeshall et al. on Oct. 17, 1967; U.S. Pat. No. 3,089,048 issued to Bahn et al. on May 7, 1963 and U.S. Pat. No. 4,126,799 issued to Iogansen et al. on Nov. 21, 1978.
For every one of the above-mentioned inventions, the existence of material creep is disadvantageous to the primary function of the coil fastener which is to provide a continuous force on the stator's end turns. Therefore, it is beneficial to have the capability of periodically retightening the device used to provide the function.
Furthermore, if the two opposing surfaces against which the clamping force is exerted are not parallel to each other, a rigid clamping device will be subjected to lateral forces which can damage it or reduce its effectiveness. For example, if a threaded stud is used and it is not perpendicular to the surface to be clamped, bending movements will be created when a nut is tightened against the misaligned pressure surface.
The primary object of the present invention is to provide an end turn bracing device which permits periodic retightening and provides a means for alignment of the device to compensate for nonperpendicularity between the bolted surface and the device.